Disinfecting means killing or inactivating pathogenic organisms and may be achieved by UV-irradiation in the wavelength range between 200 and 300 nm. Pathogenic microorganisms may cause diseases, particularly in humans. The germicidal effect of short-wave UV-radiation is based on the absorption of this radiation by nucleic acids (DNA, RNA) in the cell nucleus of the microorganisms. UV-radiation in the wavelength range of approximately 260 nm has the highest absorption rate. In the cell nucleus, this UV-C radiation causes a photochemical reaction that alters the nucleic acid structure of the microorganisms. Cell division and progeny are now no longer possible. UV-C radiation therefore makes it possible to reliably sterilize liquids, particularly drinking water. Depending on the radiation intensity, germs may be reduced by up to 99.999. In order to achieve a sufficient germ reduction for drinking water, for example, DVGW W294 specifies that the radiation dose acting upon the liquid to be sterilized must not fall below 400 J/m2.
WO 2008/050349 A2 describes an UV-disinfection system for liquids with installed monitoring options, wherein a water line features a wall that is at least partially transparent to UV-light and a light detector that is arranged in the vicinity of the light source in order to measure the light generated by the light source.
Such an UV-disinfection system consists of an irradiation chamber, through which the liquid to be sterilized, particularly drinking water, is conveyed and of one or more UV-radiators that are usually arranged in a cladding tube that is transparent to UV-light and protects the radiators from the liquid. The cladding tube usually consists of a silica glass. In order to monitor the required UV-radiation intensity, one or more UV-sensors are arranged in the irradiation chamber.
Especially, drinking water may lower the transmittance for UV-radiation due to its chemical-physical parameters such as, for example, its turbidity, hardness and/or content of suspended matter, iron, manganese and humic acid. These chemical-physical parameters depend on the source, from which the drinking water is obtained. These water ingredients may also soil the UV-disinfection system or lead to deposits on the cladding tubes.
The attainable UV-radiation intensity in the irradiation chamber therefore is essentially dependent on three factors. The first factor is the power of the UV-radiator and its state of aging based on the hours of operation, the second factor is the cleanliness or the maintenance status of the cladding of the UV-radiator that surrounds the UV-radiator, and the last factor is the effective water quality with respect to its ingredients, particularly its UV-transmittance that represents the transparency to UV-light at a certain wavelength.
Particularly in the mobile use of UV-disinfection systems such as, for example, in aircraft, buses, rail vehicles or ships that obtain the drinking water intended for disinfection from different sources, reliable information on the maintenance status of the UV-radiator/cladding combination may usually not be obtained based on a measured value of a UV-sensor due to the changing UV-transmittance of the drinking water.